I found a 1990 CRX Si with a D15B 3 stage swap for sale. The guy says that he bought the car not running. He got it to run and eventually pulled out one of the o2 sensors (there's two?) because they looked like junk and he says it ran better afterwards. But the ecu throws code 41 (primary oxygen sensor heater). He says that the car has a rough idle but I'm guessing that's because he pulled out the o2 sensor?

He also said that the car is converted to obd1. Wouldn't you need obd2 to run the D15B 3 stage? Can't he still be running the PM6 from the Si but without vtec? Or another vtec ecu and he could just have it go from 12v mode to 16v with bigger cam or 16v mode to 16v with bigger cam? Is there a way to distinguish the PM6 from the D16A6 between the P2J from the D15B?

Is there a way to figure what ecu you have without the O.E. sticker?

 

If you look at the ECU, the plugs are very different between the different OBD versions.
Very easy to just look at and know.
Obd0 is at the bottom, then obd1, obd a, and obd b on top.


The motor itself is not any particular OBD, so no to your question if it had to be OBD2. The electronics on the motor are what determine the OBD. If it's giving code 41, then it can not be OBD0, because they did not have O2 heaters. Code 41 will never appear on an OBD0 system.

If obd1 is being used on this motor, then it is not possible to run the vtec system properly unless there was some extra work done to actuate the 3 stage vtec on the motor+tuning to get it mapped correctly.
Best option is to convert to OBD2 to run the motor, but that opens up unique problems since the 88-91 chassis does not immediately support a few of gage OBD2 sensors

 

Ok, thanks. I will ask for a picture tomorrow and if I still can't figure it out, I'll post it up here.

 

Also, it is common for people to run this motor on OBD 1.
They either never hook up all the stages of vtec
Or
They get RPM activated switches to activate it.

 

Yeah, I read about just running the second solenoid and going 16v to 16v w/ bigger cam, skipping the 12v/lean burn mode. Would you just use any vtec ecu? If it doesn't work that well with the D15, could it cause rough idling? Or is a pulled o2 sensor by itself enough to cause rough idle.
I also read about how you could physically activate switches. Could be pretty cool but you would have to keep your eyes on the tach a lot if you'd want it to kick in at the same rpm every time. From what I saw and discussed with the seller, vtec is not activated by a switch.

EDIT: Maybe the idle is rough because it's setup to skip the 12v mode?

 

If you went obd2 and used the JDM ecu for this engine you'd be fine as the JDM ECUs don't look for a lot of the sensors US ECUs look for (CKF, 2nd 02, EVAP, etc). Make sure you get one for a 5 speed however and wire up both the VTEC connectors as well as EGR wiring.

https://honda-tech.com/forums/showth...636&styleid=18

 

It would be nice to have the jdm ecu but they are hard to find for a manual trans and/or they cost a lot.

EDIT: Car was sold for $600.